1. Field
This disclosure relates to a catalyst for a fuel cell, an electrode for a fuel cell, a membrane-electrode assembly for a fuel cell, and a fuel cell system using the same.
2. Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant with a hydrogen gas or hydrogen contained in a hydrocarbon-based material such as methanol, ethanol, or a natural gas.
Such a fuel cell is a clean energy source that can replace fossil fuels. It includes a stack composed of unit cells and has an advantage of producing various ranges of power. Since it has a four to ten times higher energy density than a small lithium battery, it has been highlighted as a small portable power source.
Typical examples of the fuel cell include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell using methanol as a fuel is called a direct methanol fuel cell (DMFC).
The direct oxidation fuel cell has lower energy density than that of the polymer electrolyte membrane fuel cell but has the advantage of easy handling of a fuel, being operated at room temperature due to its low operation temperature, and needing no additional fuel reforming processor. On the other hand, the polymer electrolyte membrane fuel cell has an advantage of high energy density and power output.
In the above-mentioned fuel cell system, the stack that substantially generates electricity includes several ones to several scores of unit cells stacked adjacent to one another, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly is composed of an anode (also referred to as a “fuel electrode” or an “oxidation electrode”) and a cathode (also referred to as an “air electrode” or a “reduction electrode”), which are separated by a polymer electrolyte membrane.
In the above-mentioned fuel cell system, a fuel is supplied to an anode and adsorbed on catalysts of the anode and then, oxidized to produce protons and electrons. The electrons are transferred into a cathode via an external circuit, and the protons are transferred into the cathode through the polymer electrolyte membrane. In addition, an oxidant is supplied to the cathode, which is reacted with the protons and the electrons on catalysts of the cathode, thereby producing electricity along with water.
However, the fuel cell has a performance deterioration problem due to elution and re-deposition of the catalysts or corrosion of a supporter supporting the catalysts.